The Hooded Merganser is the smallest of three North American mergansers and the only one restricted to this continent. Breeding throughout a wide area in the forested east and northwest -- where suitable nest cavities enhance adequate brood habitat -- it is most common in the Great Lakes region. Favorite winter habitats include forested freshwater wetlands, brackish estuaries, and tidal creeks. Unlike other mergansers which feed almost exclusively on fish, Hooded Mergansers have a more diverse diet, diving and capturing small fish, aquatic insects, and crustaceans, particularly crayfish, with the aid of eyes well-adapted to underwater vision.
Taxonomically intermediate between goldeneyes (Bucephala sp.) and mergansers in the genus Mergus, the Hooded Merganser shares many courtship behaviors and vocalizations with these species. Female Hoodeds first breed at two years of age and lay unusual, almost spherically-shaped eggs with disproportionately thick shells. Like other waterfowl that nest in holes, this species commonly lays its eggs in the nests of conspecifics and other cavity-nesting ducks.
The basic nesting ecology of Hooded Mergansers is relatively well known (e.g., Zicus 1990a , Mallory and Weatherhead 1993c ), particularly aspects of eggs, incubation (e.g., Zicus 1997 , Lemons 2004 ), and brood parasitism ( Mallory and Weatherhead 1990 , Mallory and Weatherhead 1993c , Mallory et al. 1998 , Dugger et al. 1999a , although almost all these data are from populations using artificial nest boxes. The longest continuous study on nesting Hooded Mergansers is from se. Missouri, where box nesting birds were monitored annually from 1968 to 2006. Recent work on population demographics ( Dugger et al. 1999b , Pearce et al. 2008 ), site fidelity and population genetics have created a clearer picture of taxonomy and population processes. Because of their trophic status, Hooded Mergansers have helped our understanding of how acid precipitation influences ecosystem processes ( Longcore et al. 1987b , McNicol et al. 1987a , McNicol et al. 1987b , Bendell and McNicol 1995b , McNicol et al. 1997 ), as well as providing evidence of the build-up of chemical contaminants in different habitats ( White and Cromartie 1977 , Zicus et al. 1988 ).
There is no reliable information on population size or status of this duck, although historically populations suffered from deforestation, hunting, and perhaps contaminants. Current evidence suggests populations are stable and possibly increasing in some areas, even though large segments of the breeding population are vulnerable to the effects of acid rain.